Consider the Polynomial x^2+x+1=0 coefficients from the set of real numbers. Let S be the set of all 2 by 2 matrices with integer entries. How many elements of S will satisfy the equation?
Yeah Peter, But I was thinking is there anything which is hidden, when I see this question, especially when the field is R and the matrices is made of integers. I just wanted to cross check, everything. that is why
The specified matrix equation leads to a system of linear equations for the elements a, b, c, d. The solution has the following form (for k=1,2,3,...): X1=[-k b; c k-1], X2=[-k -b; -c k-1], X3=[k-1 b; c -k], X4=[k-1 -b; -c -k], X1T, X2T, X3T and X4T where bc=-k2+k-1 (typically, b=k2-k+1 and c=-1 but there are more options for choosing b, c when k2-k+1 is a composite number, e.g. for k=5).
All matrix solutions are similar to the matrix D=[(-1+i\sqrt(3))/2 0; 0 (-1-i\sqrt(3))/2].